The present invention relates to a locking device for vehicle safety belts, particularly for motor cars, of the type in which a band of the belt is automatically wound onto a rotatably mounted shaft by means of a spring, when the belt is not used. The locking device is adapted to lock the shaft onto which the band is wound, so that the band cannot be further withdrawn from the shaft, and is intended to start operation due to the movements of the vehicle or due to rapid withdrawal of band from the shaft, so that a person who is embraced by the safety belt is reliably retained in case of danger.
Locking devices of the type set forth above are previously known. In the known devices, the shaft onto which the band of the belt is wound is rotatably mounted between two side walls of a support carrying the safety belt. The locking device for the shaft may comprise two notched wheels rigidly attached to the shaft and a moveable locking bar adapted to cooperate with the notched wheels for locking the shaft. The locking bar is moveable between a passive position, in which the locking bar is positioned outside the paths of rotation of the wheel notches, and an active position, in which the locking bar at least partially runs into the paths of rotation of the notches, so that rotation of the notched wheels and thus also of the shaft is prevented, thus preventing further withdrawal of band from the shaft.
Locking devices of the type set forth above in which only one notched wheel is attached to the rotatably mounted shaft are also previously known, but the use of two notched wheels has the advantage that the tractive force in the band to be transferred to the support can be transferred symmetrically to both ends of the locking means. This will facilitate the transfer of the force from the shaft to the support and therefore also the design and mounting of the locking means.
In the prior art devices having two notched wheels rigidly attached to the shaft, the notched wheels have been positioned adjacent different ones of the side walls in which the shaft is mounted and between which the band of the safety belt is wound onto the shaft. A device of this type is disclosed in the British Patent Specification No. 1 418 373. However, in such a device the locking bar must be positioned at a comparatively large distace from the coiling shaft, because the locking bar must be positioned outside the outermost turn of the coil formed on the shaft, when the band is maximally wound onto the shaft, i.e. when the safety belt is not used. Furthermore, the locking bar must have a length corresponding to the distance between the sidewalls, and the notched wheels must have a radius approximately corresponding to the distance between the axis of the shaft and the locking bar. A support for a safety belt having a locking device of this type will therefore have a comparatively large size and high weight.